Various gas detection devices are already known.
These may include devices that use physico-chemical absorption processes on a surface (for example, on tin oxide layers), these absorption processes causing a modification in a physical property (for example the number of carriers) of a material. This modification can then be detected in a simple way, for example by electrical conduction.
This type of device is very sensitive. Consequently, it is not very precise as it turns out that it does not necessarily detect the gas presumed to be present. This is because the device may for example be triggered by the moisture of the environment.
Other devices make use of absorption processes on a surface of an organic material having a chemical affinity for the gas to be detected. The detected modification may again be by electrical conduction but also by the variation in the mass of the material using a microbalance.
These devices have a major drawback due to the chemical nature of the interaction. This is because the gas remains trapped in the organic material and, over the course of time, the device losses its sensitivity.
Other devices detect gases using characteristic absorption lines of the gas sought, since gases have well-pronounced spectral signatures in the infrared that allow gases to be distinguished from one another.
The expression “spectral signature of a gas” is understood to mean the absorption spectrum which is specific thereto and which corresponds to dissipation of the light energy after the molecules of the gas have been set in resonance with the wavelength used. Energy is therefore transferred between the light wave and the gas molecules.
Thus, Lidar (Light Detection and Ranging) detection, which consists in detecting the optical scattering echo generated by an absorbent scattering pocket of gas, or photoacoustic detection, which consists in detecting the pressurization of the gas which is heated by the absorption of radiation and which expands within the cavity in which it is placed, may be mentioned.
As regards acoustic detection, the article by C. Hagleitner et al.: “CMOS single-chip gas detection system comprising capacitive, calorimetric and mass-sensitive microsensors” published in IEEE Journal of Solid-State Circuits, Vol. 37, No. 12, December 2002 may be mentioned.
In the latter case, the light radiation is absorbed by the molecular bonds of the gas and converted into kinetic energy, thereby resulting, from a macroscopic view point, in the gas being heated up. This heat-up causes a local increase in the pressure, which is detected by means of a membrane, the movement of which is measured.
A device of this type advantageously uses the specificity of the spectral signature of a gas.
However, it does have drawbacks.
Firstly, the sensitivity of the measurement depends on the area of the membrane. Thus, the possibilities of miniaturizing the detection device are considerably limited, if it is desired to obtain reasonable precision.
Secondly, such a device must be used with a closed chamber, especially a tube, in which the gas is made to flow. It is therefore necessary to provide pumping means for making the gas flow into the chamber.
The use of such a device therefore imposes restrictive operating conditions. Thus, this detection device could not be used for domestic purposes.
The object of the invention is to alleviate these drawbacks by providing a device for detecting a gas, which is compact, which ensures precise detection of the gas and which is very simple to use, thereby making domestic applications conceivable.